def Input():
    cLst = []
    print('>', end='')
    cLst = list(eval(input()))
    for i in range(len(cLst)):
        cLst[i] = int(cLst[i])
    return cLst[:]
        

def main():
    lst = Input()
    print(f'lst = {lst}')
    summ = 0
    for i in lst:
        summ += i
    print(summ//2)
    
if __name__ == '__main__':
	main()
